A poor but practical solution

So while we don't have the field experience to come up with cost of CPU as a percentage of the system or a history of CPUs used in the past, we still need to come up with an advice for the next six months or so. Our best bet in this case is probably to surf to the sites of some large vendors, e.g. HP or Dell, pick the current system of choice, step up the default CPU by two, look it up in the benchmark charts, and demand that the CPUs to be chosen from half a year ahead in time all rank higher on those benchmarks. If we do not trust ourselves on that, we may watch what others recommend. The University of Pennsylvania in the US states some sensible thoughts in their Computer Recommendations Page.